1. Field of the Invention
The present invention relates to a laser-light alignment method for adjusting alignment of laser beams emitted from a plurality of semiconductor lasers with an optical fiber in which the laser beams are to be combined (optically multiplexed). The present invention also relates to a combined-laser-light source to which the above laser-light alignment method is applied. The present invention further relates to an exposure system having the above combined-laser-light source.
2. Description of the Related Art
The following documents (1) and (2) disclose information related to the present invention.
(1) U.S patent Laid-Open No. 20020090172)
(2) Japanese Unexamined Patent Publication No. 2000-338432
Conventionally, various combined-laser-light sources are known. In the combined-laser-light sources, an entire bundle of laser beams emitted from a plurality of semiconductor lasers is converged and enters a single optical fiber so that a laser beam having a high output power is outputted from the optical fiber, for example, as disclosed in the above document (1). In addition, in various exposure systems and the like which are currently known, a laser beam is applied to a photosensitive material so as to expose the photosensitive material as disclosed on the document (2).
Incidentally, the output power of exposure-light sources is required to be increased in order to increase the processing speed in the exposure systems. In particular, in order to increase the output power of the exposure-light sources without increase in the system size, use of the aforementioned combined-laser-light sources can be considered. However, since the lifetimes of the semiconductor lasers (e.g., about 10,000 hours) are shorter than those of the exposure systems, there are demands for powering the semiconductor lasers in each exposure system only when a photosensitive material is exposed, and powering off the semiconductor lasers when no photosensitive material is exposed even during operating time of the exposure system in order to apparently lengthen the lifetimes of the semiconductor lasers.
Nevertheless, every time the semiconductor lasers are powered on, it is necessary to wait for a startup time until the output power of the combined-laser-light source becomes stable and usable (i.e., until the combined-laser-light source start up). Therefore, it is difficult to power on the semiconductor lasers only when a photosensitive material is exposed, without interfering with operations of the exposure system.
For example, in the case where a laser output power of 150 mW is obtained from a combined-laser-light source having a module in which seven laser beams are combined into a single laser beam, the applicants have experimentally confirmed that the startup time, i.e., the time elapses since powering on of semiconductor lasers until startup of the combined-laser-light source is about one minute. However, in order to power on and off semiconductor lasers in a combined-laser-light source without interfering with operations of the exposure system, it is desirable that the startup time is about one second. In addition, in order to increase productivity of the exposure system, further increase is required in the output power of the exposure system. However, it is confirmed that the startup time increases with increase in the output power. Further, in the case where a plurality of (e.g., seven) laser beams are combined in a single module, it is required that the seven laser beams do not spread wide.
Furthermore, the combined-laser-light source in which laser beams emitted from a plurality of GaN semiconductor lasers are combined into a single laser beam has a short wavelength, and is suitable for use as a light source for highly fine exposure of a photosensitive material. However, the applicants have also experimentally confirmed that a long time is necessary for the GaN semiconductor lasers to start up after the GaN semiconductor lasers are powered on.